Flow cytometry is an analytical technique used in a number of applications to measure physical and/or chemical properties of biological or non-biological particles as they flow in a sample fluid through an investigation cell, commonly referred to as a flow cell. Although the sample fluid may be investigated by subjecting the sample fluid to a variety of stimuli, light is one common stimulus technique. Scattered light exiting from the flow cell may be detected and analyzed to provide information on the characteristics of particles present in the sample fluid. Light stimulation and light detection techniques may be tailored to identification of particular characteristics indicative of the presence of particular types of particles. For example, one technique is to stain a sample fluid with one or more stains (also referred to as dyes) that associate with a particular biological component of interest. The stains may have fluorescent activity that provides a fluorescent emission in a particular wavelength range, the detection of which provides an indication of the presence of that biological component. For example, two different fluorescent stains, one that associates with protein and another that associates with nucleic acid, may aid in the detection of virus particles. Light detection may be designed to specifically detect light at the different fluorescent emission wavelengths of different stains. This may involve splitting light received from the flow cell into different light wavelength ranges, such as using a dichroic mirror that passes some wavelengths of light while reflecting other wavelengths of light.
Devices for performing flow cytometry are referred to as flow cytometers. Flow cytometers are often designed to optimize detection of a specific type of particle, for example specific cells, bacteria or virus. A complicating issue for flow cytometer robustness and durability over a prolonged period is that flow cytometers tend to be very sensitive instruments that require very precise alignment of optical elements for optimal performance. Flow cytometry optical elements, which may include a light source, a flow cell, lenses, beam splitters and light detectors, are typically precisely located and secured in place in the flow cytometer with a desired alignment within and protected by a protective enclosure, or shell. To provide some ability to fine-tune alignment of the delivery of light to the flow cell, a light source, such as a laser, may be mounted on an adjustable mount that permits some adjustment of the positioning and orientation of the light source to permit some fine-tuning of the alignment with the flow cell or with a lens disposed between the light source and the flow cell.
Even with optical components firmly secured in place, flow cytometers are susceptible to significant performance degradation during operation from even slight physical environment disturbances such as ambient vibrations, including incidental bumps or mechanical shocks, and are susceptible to significant loss of performance over time from even slight changes in the alignment of optical elements that may occur over a prolonged period. These performance degradations may be even more problematic for flow cytometers that are operated to detect extremely small particles, such as virus particles. Maintaining a high level of performance may involve frequent and expensive servicing of a flow cytometer. In addition, significant degradation of optical element alignment and damage to fragile equipment may occur during shipping and handling operations, which may limit the range of equipment that may practically be used and/or may require significant servicing of the flow cytometer on-site after shipping and prior to use.